I've made 2 versions the advanced one has a lot of categories like minerals and vitamins, and the basic one is just the major nutrients protein, fat, fibre and carbs. You can switch between them using the little tabs at the bottom.
The colour code I used in the food list goes flour seed, oil seed, protein, legume, and vegetables you don't need to keep it the same but the categories calculate the percentage of that of the diet so you can get your flour seed to oil seed ratio correct. This is also useful if you are trying to combine two commercial mixes.
All the light purple is where you would add the nutritional information for the food and dark purple is the amount of food you want to add to the mix.
Don't add any data into the blue cells they all have formulas and you don't need to change them.
I've included in the spoiler how to convert the data from a food label into grams/100g as that's what I've used as units, but you can use what you want and ignore this section.
That being said Here is the copy of my spreadsheet. On a brand new google account because apparently, you can't share stuff on google without all your details being out there.
To use this copy and paste the whole thing into a blank copy of google sheets and add in the data you need.
Spoiler
Uk food labels are quite simple most of them have a per 100g column. The first data column on this spreadsheet is the amount per 100g so the product has 1.5g/100g of fat and 7.7g/100g of protein.

This label is a bit harder as the amount total is 208g, not 100g. So 208g of food contains 4g of fat.
4 parts of 208 grams are fat
4/208= 0.01923077
To get how many parts of fat per 1g of food
Then multiplying by 100 to get how much per 100g
0.01923077X100=1.923

If the label only has ounces multiply that value by 28.35 to get the weight in grams.

This label is a bit harder as the amount total is 208g, not 100g. So 208g of food contains 4g of fat.
4 parts of 208 grams are fat
4/208= 0.01923077
To get how many parts of fat per 1g of food
Then multiplying by 100 to get how much per 100g
0.01923077X100=1.923

If the label only has ounces multiply that value by 28.35 to get the weight in grams.





